Measuring instrument for alternating currents.



Patented out. 30, |900.

- K. 0. F. scHnoTTKE. I

MEASURING INSTRUMENT FOR ALTERNAT'HCG GURBENTS.

(Apnlicntion led Sept. 2 1899.)

(Ho madam'.

'fig j.

mi C UNITED STATES PATENT OFFICE.

KARL OTTO FRANZ SCHROTTKE, OF BERLIN, GERMANY, ASSIGNOR TO THE SIEMENS it HALSKE ELECTRIC COMPANY OF ILLINOIS.

AMERICA, OF CHICAGO,

MEASURING INSTRUMENT FOR ALTERNATING CURRENTS.

SPECIFICATION forming part of Letters Patent No. 660,804, dated October 30, 1900.

Application filed September Z, 1899. v Serial No. 729,324. (No model.)

To all whom t may concern.-

Be it known that I, KARL O'r'ro FRANZ SCHROTTKE, a subject of the Emperor of Germany, residing at Berlin, Germany, have invented a certain new and useful Improvement in Measuring Instruments for Alternating Currents, (Case No. 221,) of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

My invention relates to measuring instruments for alternating currents operating through the agency of rotating fields, and has for its object the elimination of certain harmful defects due to abnormal driving or retarding forces which are frequently present in instruments of this class and which in the ideal instrument should not be present. These disturbing forces are in a great measure due to friction and bad .workmanship and materially detract from the accuracy and sensibility of the instruments. tion are noticeable in their retarding influence, being much more so Where countingtrains are used. The inaccuracy due tthese abnormal forces may occur in all instruments of the class described. In all indicating-wattmeters of the class mentioned additional and abnormal driving forces may be caused either by the pressure-coil alone or by the currentcoil alone, tending in the first case to displace the indicator from its zero position at no load and in the second case to change the constant of the instrument in proportion to the magnitude of the exerted forces. Where interiorly-disposed iron cylinders or bodies are employed, these faults are frequently due to their eccentric mounting. of means for correcting or compensating for these errors is the object of my present invention.

I will point out my invention in the claims and fully explain the same by reference to the accompanying drawings, illustrating one embodiment of the invention,-in Which- Figure 1 is a View of one type of instrument embodying my invention. Fig. 2 is an enlarged view of a part thereof. Fig. 3 is a dia- The effects of fric- Y The provisionV gram for demonstrating the electrical princi- 5o ples here involved. Figs. 4, 5, 6,and 7 are views of anumber of modifications of my invention. i

Like letters of reference refer to like parts in the different figures.

Instruments operating through the agency of rotating fields may be made, for example, as shown in Fig. l. My invention is particularly applicable to instruments of this construction, but is alsoA useful in connection 6o with instruments of other construction.

The outer or stationary part of the instrument shown consists of an iron eld-ring a, built preferably of lamina of magnetic material and has four equidistant internal radially-projecting pole-pieces b b and c o. A metal drum d is rotatably mounted inside and concentric with the ring ct at a short distance fromthe ends of said pole-pieces. An iron cylinder e is placed inside and concentric with 7o the drum and at a short distance therefrom.

A series Winding through which the main current flows is placed upon the pole-pieces b b, and a shunt-winding carrying current which may be displaced ninety degrees from the impressed pressure is placed upon the polepieces c c. If the shunt-Winding alone conveys current, then two principal paths for lines of force will be opened through the ring. The centers of these separate paths Mg Mk 8o are symmetrically arranged and no forces will be exerted on the drum, providing no abnormal forces exist. They may, however, exist, and to counteract the same by adjusting the reluctance in one or the other of said paths is the object of my invention. y If the reluctance in either path beincreased, which is preferably done by cutting a Igroove f of any desired cross-section on the periphery7 of the inside ring, a force will be exerted on the 9o drum whose strength is dependent upon the relative positions of the groove and the polepieces, whereby the error may be corrected.

i The effect of the adjustment will be more readily understood by reference to Fig. 2, Whe re a section of the outer field-ring, including the pole-piece c, is shown in conjunction with the metal drum andthe grooved core.

f. 'must be placed near the shunt-poles.

If the inner cylinder e be placed so that the groovevf covers one-half'of the pole-piece opposite the points g h, the reluctance in the path of the line Mg, threading this grooved portion, is greater than the reluctance of the path of the line Mk, threading the unchanged portion of the inner cylinder. The line Mg will therefore be weaker and will induce a lesser current in the drum than the line Mk. The total current 7l of the shunt field-coils, Fig. 3, has two components-the active current t', and one at right angles thereto, the wattless current im. The active current is in phase with and equal to the current which is inducedin the drum, while the wattless currentcreates the shunt-iield M. The other shunt-field M,r is less than the shunt-field Mk and will therefore induce the correspondingly small currentin the drum. For this reason the active componentjfy of the total currenti must be less than the active component in the rst case. For this reason the wattless component Mg must be larger, and such may only be the case if the active component jt in the second case is displaced in phase from the active component t by an angle a. As the two magnetic lines of force Mg and Mk form the sides of an angle the turning forces exerted upon the drum will be proportional to the expression Mg Mk sin. as The direction of rotation in this case will be clockwisethat is, from the point g to the point ire-as the lines of force Mg reach their maximum sooner than do the lines of force Mk. By rotating the iron cylinder until the groovef is shifted into the position indicated in dotted lines the line of force Mk will be reduced and will precede the line of force Mg, thereby changing the direction of the lturning moment. YThe direction of rotation may be gradually reversed and the force of the turning moment graduallyvaried by the gradual rotary movement of the cylinder e. The groove has no appreciable effect in the apparatus shown after being removed from a polepiece. So long as the groove is not placed underneath the series winding its action is independent of the working circuit. One

groove would bevsnfticient, but by the use of two the effect is doubled. The form of groove may be any desired, several illustrations of the many types being shown in Figs. 4., 5, 6, and 7. To permit of an easy adjustment, I preferably provide an arm Z, as shown in Fig. l, which serves to rotatably adjust the cylinder e, which adjustment may be secured by the screws n n. If the friction in the meters is to be overcome, the grooves f This also should be done in securing proper reading (zero reading) upon ino load. If the con'- stant of meters changes with the change of load, it is necessary to bring vthe grooves within the sphere of action of the series field, as such eects are always theresult of inaccurate action of the series field. Where two adjustments are to be effected with Vrelation totheseries and shunt poles, I prefer 'to shape the poles in the body e as shown in Fig. 5.

It is obvious that changes may readily be made in the method and apparatus of my invention without departing from its spirit, and I do not therefore desire to be limited to the precise embodiment of the invention particularly described; b ut,

Having described my invention, I rlaim as new and desire to securevby Letters Patentl. In an alternating-current-measuringinstrument, the combination with the movable member, of a field portion, a winding therefor for association with an alternating-current circuit, and an adjustable portion included in the same magnetic circuit with the field portion adaptedk to vary the reluctance of a portion only of the magnetic circuit including the lield portion substantially as described.

2. Iu an alternating-current-measuring instrument, the combination with the movable member, of a field portion, a winding therefor for association with an alternating-current circuit, and a rotatably-adjustable p0rtion included in the same magnetic circuit with the field portion adapted to vary the reluctance of a portion only of the magnetic circuit including the field portion substantially as described.

3. In an alternating-current-measuring instrument, the combination with an alternailing-current circuit, of a winding, a field portion affording multiple magnetic circuits for the lines 'of force due to the said winding, means for varying the reluctance in one of said magnetic circuits, and a movable element of the instrument subjected to the action of said field portion, substantially as described.

It. In an alternating-current-measuring instrument, the combination with a winding to be ass'bciated with an altern atin g-current circuit, ot' a field portion affording distinct paths for lines of force due to the said winding, a movable element of the instrument subjected to the action of said field portion, and a rotatable `body for effecting the adjustment of the reluctance in said magnetic circuits or either of them, substantially as described.

5. The combination with an annular field portion provided with inwardly-projecting pole-pieces, of 'a winding for the iield portion, an armature subjected to the action of the field portion, and an adjustable magnetic body inclosed by the armature adapted to effect the adjustment of the reluctance in the magnetic circuits threaded bya portion only of the lines of force, substantially as described.

6. In an alternating-current-measuring instrument, the combination with afield-ringe provided with interiorly projecting polepieces h b 'c c, of windings for the said polepieces, a dr-u-m d inclosed by the pole-pieces,

IOO

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and an adjustable grooved iron cylinder e and a grooved iron eyiindere inciosed by the inclosed by the drum, substantially as described. 1

7. In an alternating-eurrent-measuring instrument, the combination with a, field-ring a, provided with interiorly projecting polepieoes b b c c, of windings for the said polepieces, a drum d inelosed by the pole-pieces,

drum, substantially as described. I0 In witness whereof I hereunto subscribe my name this 15th day of August, A. D. 1899.

KARL OTTO FRANZ SCHROTTKE. Witnesses:

HENRY HASPER,

WILLIAM MAYNER. 

